1. Field of the Invention
The present invention relates to a method for determining the volume of a tubing system connected to a ventilator and to a patient. The present invention also relates to a method for determining an elastic volume of a tubing system connected to a ventilator and to a patient. The present invention also relates to a breathing apparatus system intended for use in the respiratory care of a patient and including a ventilator and a tubing system.
2. Description of the Prior Art
The ability to determine and/or regulate the amount of breathing gas supplied to a patient is important in respiratory care. Determined and/or regulated volume is usually stipulated in volume per breath (tidal volume) or average volume received per unit of time (minute volume) Breathing gas is usually supplied to the patient by a ventilator and a tubing system. Since gases are compressible (elastic), the volume of gas in the tubing system must be taken into account. As a rule, the tubing system is also elastic, so the actual volume in the tubing system can vary with the pressure. Studies have shown that the mechanical elastic volume can constitute 25-40% of the total elastic volume.
Testing a breathing apparatus system (e.g. a ventilator and tubing system) before the patient is hooked up to it is common. Compensation for the elastic volume can then be made by an operator. This is particularly important when a specific tidal volume must be supplied to the patient in each breath.
It would be advantageous if these measurements also could be performed while the patient is connected to the breathing apparatus system for respiratory care, since conditions could change in the course of treatment. Changes might develop especially in peripheral devices, which constitute dead space for the system, such as humidifiers, dehumidifiers and nebulizers.
A major problem is to exclude the patient from volume determinations. Determinations would be erroneous if the patient's airways and lungs were allowed to interact with the tubing system during a volume determination.
Another problem is to establish total elastic volume in an effective fashion.